Ultra wideband (UWB) has emerged as one of the most promising wireless systems recently for several reasons. Firstly, its multi-path resistance results in better power transmission efficiency. Secondly, its low average power spectral density causes less interference to other services sharing the same band. Thirdly, it is capable of precise location positioning.
Nowadays, there are many different UWB spectrum and regulatory approvals in the world. The US Federal Communications Commission (FCC) has utilized the 3.1 to 10.6 GHz band; the European Communications Commission (ECC) has announced support for the 6 to 8.5 GHz band, while Japan looks set to ratify the 7 to 10 GHz band. In order to accommodate various different UWB spectrum regulations, a UWB pulse generator with programmable UWB pulse center frequency and −10 dB bandwidth is desired.
UWB pulse generation is critical for an impulse radio (IR-UWB) system. Current IR-UWB pulse generation methods fall into four main categories. One approach is to generate a pulse at baseband and then up-convert to the target frequency band. These carrier-based designs tend to have complex architectures, high power consumption and LO leakage problem due to the need of a local oscillator. A second approach is to generate pulses directly in UWB band. This approach usually requires additional pulse shaping using high order band pass filter (BPF) which occupies large area, and is harder to be programmable. In a third approach, a new waveform synthesis method based on high-speed digital-to-analog converters (DAC) was proposed for UWB pulse generation. It has both good time and amplitude resolution, and can generate different pulses with different center frequencies and −10 dB bandwidths. However, high sampling rate is required, which will result in large circuit complexity and power consumption. A fourth approach is to combine different delay edges with the polarity controls to form a very short duration “logical” pulse, which is then filtered so as to obtain an UWB pulse. With this approach, the center frequency and −10 dB bandwidth of the pulse can be programmed by varying the delay between edges and the number of edges combined.
There is a need to provide a UWB pulse generating circuit which is programmable with reduced circuit complexity and with large peak power.